The present invention relates generally to steering wheel assemblies having air bags and, more particularly, to a cover for an air bag of a steering wheel assembly.
Air bags typically are located beneath a cover of a steering wheel assembly. Historically, the steering wheel was attached to the vehicle and then the air bag module, which included a cover attached over the air bag, was attached.
A steering wheel and air bag assembly includes a cover, a steering wheel armature and an air bag. Most covers are formed of a synthetic plastic material that is positioned over the air bag cushion. The cover is generally attached to the steering wheel assembly by rivets. In order for the air bag to deploy properly, it is necessary to provide a thinned portion for the air bag to break through the cover. Typically, the thinned regions included tear seams located in the cover that had generally been either H-shaped, I-shaped, U-shaped or branched shapes as viewed from the driver's seat.
The branched shapes of the tear seams require more energy and time to tear, thus the air bag must be deployed with a very high force for it to deploy and inflate rapidly enough to serve as a crash restraint. In addition, the high force used during deployment can cause the cover to break in high stress regions, resulting in reduced integrity of the air bag module. Additionally, the high deployment forces can lead to cracking or tearing of the module cover. Furthermore, these tear seam designs limit the area of opening in the cover and tend to cause the air bag to deploy straight outward rather than outward and to the sides. By allowing the air bag to expand quickly to the sides, the air bag inflates with less force and more efficiency.
The rivets used to couple the cover to the air bag housing require very labor intensive assembly procedures. Further, the rivets produce a high stress concentration interface between the cover and the air bag mounting plate, which can provide crack initiation sites. Air bag modules having an H-shaped or U-shaped cover experience significant stresses on the door hinges caused by inertial forces from the rotating of the door mass. As such, it is desirable to provide a cover design that enables the air bag cover to be retained without rivets with ensured integrity after deployment. It is also desirable to provide a tear seam that ruptures more rapidly and that will deploy in response to a lower inflation force.
The present invention provides a steering wheel assembly that receives a fastenerless air bag cover assembly that increases the integrity of the air bag module after deployment. This assembly employs a housing with a projection and a steering wheel armature configured to receive the projection. The cover is retained between the housing and the steering wheel armature. In addition, the present invention provides an air bag cover with a tear seam that permits the air bag to deploy more efficiently with less stress to the module. Specifically, the cover has a circular center from which at least one tear seam radiates. The tear seam ends at an articulated terminus.
These and other features and advantages of this invention will become more apparent to those skilled in the art from the following detailed description of the presently preferred embodiment. The drawings that accompany the detailed description can be described as follows.